Nearly Phase Of Close Binary Observation And Study

In the first section of the present paper, the definition, classification and some observational characters of near contact binaries are introduced. Further more, some methods about photometric study of near contact binary are simply illustrated. In the second section, based on the analyses of observations of three systems: IK Per, IR Cas and BL And, some results are concluded as follows:1 Using the 1.0-meter Cassegrain reflector telescope at Yunnan Observatory, we obtained the first complete CCD light curves of IK Per in V and B band respectively. In the forth edition of GCVS, the light variation of IK Per was classified as EB/EW type, but we found that the light curve is typical EW type with nearly of two minima and negative O' Connell effect. With the observed data, three times of light minimum were derived. Combined with the available minima, the period study of IK Per was done. The results show there are two possibilities for the period variations: one is a secular period decrease withdp/dt=-2.68×10-7 days/year, the other is the sudden period decrease with 1.15saround E=28000.2 Using the 85-cm telescope at the Xinglong Station of National Astronomical Observatory, we obtained two times of light minimum of IR Cas. Compiled all available times of light minimum, we studied the period of this system. It was discovered that a periodic oscillation with a period of 53.24 years and amplitude about 0.0133days is superposed on the secular period decrease ofdP/dt = -1.18×10-7 days/year. If the period decreases at this rate all the time in thefuture, IR Cas will evolve into a contact binary after 2.39×106 years. The reasons of the secular decrease may be caused by the mass transfer between the two components or/and angular momentum loss from the system. On the other hand, the periodic changes in the orbital period can be attribute to magnetic activity cycles in the two components or to the light-time effects of an additional body.3 Using the 85-cm telescope at the Xinglong Station of National AstronomicalObservatory, a complete light curve in V and two times of light minimum were obtained. With all available eclipse times, we studied the period change of this system. It is found that the orbital period of this system exists secular decrease withdP/dt = -2.63×10-8 days/year. The light curve is analyzed by means of theWilson-Devinney code, and the present photometric solution reveals that BL And is a marginal contact binary system with a dark spot on the photospheric surface of the second component. The secular period decrease and the marginal-contact configuration both suggest that BL And will evolve into a normal contact binary system. The reasons of secular period decrease may be caused by the mass transfer from the primary to the secondary component or/and the angular momentum loss from this system.